Composite materials comprising a plurality of resin impregnated felt layers

ABSTRACT

Composite materials are provided which include one or more felt layers, impregnated, in a compressed state, with a reinforcing polymeric resin, e.g., a water-borne phenolic resin. The composite material may further include other layers, e.g., a fibrous layer such as glass cloth or scrim.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. Ser. No.08/177,562, filed Jan. 5, 1994, now U.S. Pat. No. 5,527,598, which was acontinuation-in-part of U.S. Ser. No. 08/057,620, filed May 5, 1993, nowabandoned.

BACKGROUND OF THE INVENTION

The invention relates to composite materials which are suitable for usein the passenger compartment of a commercial aircraft.

It is well known to use composite materials that include, e.g., glassfabric or nonwoven material which is coated or impregnated withpolymeric resins, for forming structural elements and, in particular,non-load bearing structural elements. Advantageously, these compositestypically replace heavier or more expensive materials. However, incertain environments, e.g., within the passenger compartments of modernaircraft, such composites are often unable to meet stringentrequirements of strength and performance established for the safety ofthose within such aircraft. These requirements may be particularlystrict where there is a perceived danger of fire. It is well-known thatthe performance of certain polymeric-based materials may beunsatisfactory, or even life-threatening, for reasons of heat release,flammability, smoke release and/or toxic gas release, and also for lackof strength, impact resistance and compression resistance, making thesematerials unsuitable for use in environments where they might otherwiseprovide a substantial benefit.

In certain environments, conventional composites also may transmit anundesirable level of heat and/or sound. For instance, there is a need inthe aircraft industry for panelling and ductwork having acousticalproperties which will minimize the noise level within the passengercompartment to improve passenger comfort. Many composites providesub-optimal acoustical insulation.

Finally, it is desirable that composite materials have good moldability,i.e., can be formed into complex shapes without wrinkling or othermolding problems.

SUMMARY OF THE INVENTION

It has been found that the degree of sound or heat transmission througha composite material can be lessened by the incorporation into thecomposite of a layer of felt material that is impregnated, in acompressed state, with a reinforcing polymeric resin. During manufactureof the composite, the felt material is saturated, in an uncompressedstate, with a polymeric binder, after which the saturated felt materialis compressed, driving out trapped air and resulting in a dense feltlayer carrying a relatively high level of reinforcing resin.

Preferred composite materials of the invention, in the presence of fire,exhibit levels of heat release, flammability, smoke release and toxicgas release that are below predetermined levels considered suitable foruse within the passenger compartment of a commercial aircraft.

Preferably, the composite material includes at least one outer wall of afibrous woven or non-woven web or fabric. This outer wall is coated orimpregnated with a reinforcing polymeric resin and bonded to the feltlayer(s). Preferably, the reinforcing polymeric resin is a phenolicresin. Both the felt and the fibrous layer may include fibers from thegroup selected from carbon, graphite, KEVLAR, glass, aramid, andmixtures thereof. Most preferably, the felt includes predominantlyaramid fibers, with other fibers added as desired to enhance themechanical and/or acoustical properties of the felt, and the fibrousouter layer comprises a glass fabric or scrim.

In a particularly preferred aspect, the composite includes a pluralityof felt layers which are laid up at angles with respect to each other,i.e., each felt layer comprises a plurality of fibers having apredominant fiber direction and the felt layers are arranged so that thepredominant fiber direction of each layer is at an angle with respect tothe predominant fiber direction of the immediately adjacent felt layers.Preferably, the composite includes four felt layers, and each felt layeris disposed at a 90 degree angle with respect to immediately adjacentfelt layers. In this embodiment, the composite material exhibitsexceptional moldability and flexural strength.

In another particularly preferred aspect, the polymeric resin with whichthe felt layer is impregnated is a water-borne phenolic resin. The useof a water-borne resin, rather than a conventional organic solvent-basedresin, allows the use of a very dilute resin solution without theenvironmental/safety problems occasioned by high levels of organicsolvent. The inventors have found that by impregnating the felt layerwith a dilute aqueous polymer solution, a controllable level of resincan be absorbed by the dense felt material.

Other preferred embodiments include the following features. Thecomposite can include a barrier to render the composite impermeable tothe flow of air, preferably selected so that the maximum flow of airthrough the composite sandwich, with a pressure differential of 20 psithereacross, does not exceed 0.005 ft³ /min/ft². The barrier film maycomprise a metallic film, e.g. aluminum, or a polymeric film, e.g.consisting essentially of polyvinylidene fluoride (PVDF). The compositemay also include, in addition to or instead of the barrier layer, adecorative layer. The reinforcing polymeric resin preferably compriseschemical agents adapted to reduce the rate of heat release, morepreferably those selected from the group consisting of aluminumtrihydrate and zinc borate. In preferred embodiments the compositematerial has a peak heat release rate of approximately 50 kw/m² and atwo minute heat release of approximately 50 kw-min/m² when tested inaccordance with the requirements of FAR 25.853(a-1) through Amendment25-66 and FAR 121.312(a)(1) through Amendment 121-198. More preferably,the peak heat release rate is less than 45 kw/m² and the two minute heatrelease is less than 45 kw-min/m². Preferably, the composite has a totalweight of less than about 32 oz./yd², more preferably less than about 30oz./yd².

According to another aspect, the invention features a method for forminga composite material which, in the presence of fire, has levels of heatrelease, flammability, smoke release and toxic gas release belowpredetermined levels considered suitable for use within the passengercompartment of a commercial aircraft. This method includes the steps ofproviding a layer of felt, impregnating the felt layer with polymericresin binder and applying a fibrous web or cloth to one or both outersurfaces of the layer of felt. If the composite includes more than onefelt layer, the layers are preferably individually impregnated withpolymeric resin, the carrier (water) of the polymeric resin evaporated(preferably by heat drying), and the impregnated and dried ("b-staged")layers laid up at angles with respect to each other, preferably at rightangles to each other. The method preferably further includes the step ofapplying heat and pressure to cure and bond the layers to form thecomposite material.

Preferred embodiments of this aspect of the invention may include one ormore of the following additional features. The method may furtherinclude the step of coating or impregnating the fibrous web or clothwith a polymeric resin before applying it to the felt layer. The methodmay further include the step of applying a barrier film, e.g. apolymeric material, preferably consisting essentially of polyvinylidenefluoride, in the region of one or both outer surfaces of the compositematerial to render the composite material impermeable to air. The methodmay include applying a decorative layer to a surface of the composite.The barrier film and/or decorative film may be applied either prior to,during, or after the bonding step. The method may include the furtherstep of molding the composite material to a desired curvilinear shape.The felt and the other layers of the composite material can be securedtogether by needling or stitching, in addition to bonding.

Objectives of the invention include to provide a composite materialwhich, in the presence of fire, has levels of heat release,flammability, smoke release and toxic gas release below predeterminedlevels considered suitable for use within the passenger compartment of acommercial aircraft.

These and other features and advantages of the invention will beapparent from the following description of presently preferredembodiments, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an aircraft passenger compartmentequipped with structural, non-weight bearing composite materials of theinvention;

FIG. 2 is a somewhat diagrammatic side view of one embodiment of acomposite material of the invention;

FIG. 3 is a somewhat diagrammatic exploded perspective view of the wallof another embodiment of a composite material of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the passenger compartment or pressure shell 2 of amodern commercial jet aircraft 4 is provided with improved structural,non-weight-bearing composite materials of the invention, including,e.g., air-conditioning duct 6, ceiling panels 8 and wall panels 10.

According to preferred embodiments of the invention, composite materialssuitable for use within the passenger compartment of a commercialaircraft are formed, at least in part, of first and second walls formedof a web of random or oriented non-woven or woven glass fibersimpregnated with a low heat release polymeric binder containing achemical flame retardant, with an intervening layer, or a plurality ofintervening layers, of felt material disposed therebetween.

Referring to FIG. 2, a composite material 12 according to one embodimentof the invention has a first wall 14 and a second wall 16, with anintervening layer 18 of felt disposed therebetween. Preferably, thefirst wall is of glass cloth and the second wall is of glass scrim,although both could be of any suitable fibrous cloth, scrim, ornon-woven web. The cloth layer preferably contains from about 30 to 34percent resin, most preferably about 32% resin; the scrim layerpreferably contains from about 36 to 40 percent resin, most preferablyabout 38 percent resin. The felt layer, in this embodiment, preferablyhas a thickness of from about 0.150 to 0.190 inch, most preferably about0.160 inch, prior to processing and curing, and contains from about 28to 32 percent resin by weight, most preferably about 30% resin. Higherlevels of resin will enhance the mechanical properties of the composite,but will also increase its heat release; similarly, lower levels ofresin will reduce the heat release of the composite, but will also tendto impair its mechanical properties. Preferred levels of resin for agiven application can be determined based on the balance of propertiesdesired.

The felt material is preferably formed of aramid resin fibers,commercially available from DuPont under the tradename NOMEX. Thesefibers have a low heat release, and thus the felt layer is able to workin combination with the wall elements to maintain acceptably low levelsof heat release in the composite material. Preferably, the fibers have adenier of from about 1.5 to 2 and a staple length of from about 2 inchesto 3 inches. The felt layer serves also as a heat insulator for anyvariation of temperature across the composite material, and as a soundinsulator to reduce the acoustic level across the composite material.The felt may be formed by conventional carding and needle loomprocessing. The density of the felt is a determining factor in theamount of resin that the felt will be capable of absorbing. Thus, thefelt-forming process should be carefully monitored to ensure that thedensity of the felt is such that the felt is capable of absorbing theamount of resin necessary to give the desired properties for a givenapplication. The factors that influence felt density are: the denier andlength of the fiber; the carded batt weight; and the needle loomprocessing parameters, i.e., the needle size, depth of penetration,number of penetrations per linear inch; and number of passes through theneedle loom. The control of these factors to obtain a desired feltdensity is well known in the textile art.

Suitable reinforcing polymeric resins are those which have low levels ofheat release. A preferred resin is a phenolic resin selected to have aslow a heat release as possible. More preferably, the phenolic resin iswater-borne, rather than dissolved or suspended in organic solvent. Asuitable water-borne phenolic resin is available from Georgia Pacific,and contains approximately 76% solids by weight. When impregnating thefibrous layers (e.g., glass scrim or cloth), this 76% solids aqueoussuspension is preferably used as supplied (small amounts of water may beadded for ease of processing, but this does not significantly affect theresulting resin content of the impregnated fibrous layer), while whenimpregnating the felt layer it is preferred that the suspension bediluted with water to about 26% solids, or a viscosity of about 15 cps.The solids level of the suspension used to impregnate the felt layer canbe varied to compensate for the density of the felt, i.e., for a higherdensity felt layer, a lower viscosity, lower solids level suspension canbe used to achieve better penetration of the felt. For example, for a0.160 inch thick felt having a density of 10-12 oz/yd², 100% water isused, whereas for a 0.050 inch thick felt having a density of 4 oz/yd²,175% water is used.

The fire retardant agents that are preferably combined with the resinmay comprise one or more components that act to reduce the heat releaserate in a manner common to the state-of-the-art. Examples of suitablefire retardant agents and/or compositions include alumina trihydrate,zinc borate and similar chemicals. Generally, the fire retardant agentsare only included in the fibrous (non-felt) layers of the composite, asthe low-solids resin suspension used to impregnate the felt layer(s)tends to be too low in viscosity to suspend most fire retardant agents.However, if they can be adequately suspended in the impregnating resinsuspension, these agents may be included in the felt layers as well.

Another embodiment of the invention is shown in FIG. 3. In thisembodiment, the composite material includes a plurality of felt layers18 (four layers are shown). Each layer is positioned so that thepredominant direction of the fibers in that felt layer is at an anglewith respect to the predominant direction of the fibers in any adjacentfelt layer. Preferably, as shown, the felt layers are positioned suchthat each is at an 80-100 degree angle, more preferably a 90 degreeangle, with respect to its adjacent layers. It is preferred that when aplurality of felt layers are used, each layer is relatively thin. Forexample, when four layers are used, as shown, preferably each layer hasa thickness of from about 0.045 inch to 0.055 inch, most preferablyabout 0.050 inch. It is also preferred that each layer contain fromabout 30 to 34% resin by weight, most preferably about 32% resin. Asdescribed above, the desired amount of resin will vary depending uponthe balance of mechanical strength and heat release needed in a givenapplication. In this embodiment, the first and second walls 14, 16 arepreferably both formed of glass cloth, which preferably contains fromabout 30 to 34% resin by weight, more preferably about 28% resin.

A polymeric film 36, e.g., polyvinylidene fluoride or nylon film about0.001 to 0.002 inch thick, renders the composite wall impermeable toflow of air (reduced air impermeability, or complete impermeability toair, is desirable in construction of ducts). A suitable polyvinylidenefluoride film is commercially available from DuPont under the tradenameTEDLAR. The film may be bonded to other components of the composite thatare impregnated or coated with phenolic resin upon application of heatand pressure during the molding operation, or may be applied later,after the composite material is cured, using adhesive or other knownmethods. The polymeric film, e.g., polyvinylidene fluoride, may be givena primer coat of phenolic resin to enhance mechanical bonding. The nylonfilm is known to solvate with the phenolic interface of the adjacentpre-preg layer to form a chemical bond that improves most mechanicalproperties, providing, e.g., improved flexing, impact and shatterresistance, and hoop strength; however, it is important to limit thedegree of solvation in order to maintain a desired level ofimpermeability. The polymeric film may be embossed and/or printed tohave a decorative effect, e.g., when the composite material is intendedfor use as panelling in the passenger compartment of an aircraft.

A layer of metallic film 38, e.g. an aluminum film 0.0007 to 0.0016 inchthick, can be included to render the wall impermeable and to reflectheat, thus lowering the heat release characteristics of the compositematerial. The metallic film may also be given a primer coat of phenolicresin to enhance mechanical bonding.

Composite materials of the invention are preferably formed by applying asolution or suspension of the reinforcing polymeric resin to each layerindividually, running that layer through squeeze rollers or the like tocause the resin to impregnate the layer, oven drying each layer at atemperature of from about 65° to 77° C. to drive off the solvent/waterand "b-stage" the layer, laying up the layers in the desiredarrangement, and heating at a temperature of about 150° C. and apressure of about 15 psi to cure and bond the layers to form thecomposite material and to force trapped air and any remaining water outof the felt layer(s). Preferably, the composite is compressed to asufficient extent so that its final thickness will be from about 0.035inch to 0.100 inch thick. As the composite becomes thinner, it will tendto become more rigid and board-like. As noted above, the barrier and/ordecorative layers can be applied either during the laying up step, orafter curing using an adhesive of the like. Also, the layers can bestitched or needled together prior to bonding, to facilitate handling animprove bond strength.

The following examples are intended to illustrate the invention, and arenot intended to be of limiting effect.

EXAMPLE 1

A composite lay-up was formed by laying up, in the following order, onelayer of style #120 glass cloth prepreg, one layer of 0.160 inch Nomexfelt prepreg, and one layer of style #3701 glass scrim prepreg. Theglass cloth and glass scrim prepreg layers were impregnated with aGeorgia Pacific water borne phenolic resin having a solids level of 76%.The cloth layer contained about 32% resin; the scrim layer containedabout 38% resin. The felt layer had a density of about 5.7 pcf, and wasimpregnated with the same water borne phenolic resin, diluted with waterto a solids level of about 38%. The prepreg layers were formed by ovendrying the impregnated layers at a temperature of approximately 70° C.

The composite lay-up was placed between two aluminum caul plates, havinga mold release applied to the surfaces which would make contact with thecomposite, and spacers of a thickness of 0.090 inch were also placedbetween the caul plates to act as stops to regulate the finishedthickness of the composite. The caul plate, composite, and spacerassembly were then placed in a heated platen press at a temperature of300° F. The platen press was then closed and maintained at a pressure of15 PSI and 300° F. for a time period of 30 minutes.

The resulting composite demonstrated a weight of 27 02/YD² and OSU heatrelease valves of: peak HRR=45.2 and 2 minute HRR=43.3

EXAMPLE 2

A composite lay-up was formed by laying up, in the following order, onelayer of style #120 glass cloth prepreg, four layers of 0.050 inch thickNomex felt prepreg, with each layer being oriented at 90° to the machinedirection of the previous layer, and one layer of style #120 glass clothprepreg.

The method used to form each prepreg layer, and the composite set-up andcuring process was identical to that of Example 1, except that the resindispersion used to saturate the felt layers has a solids content ofabout 26%, rather than 38%.

The resulting composite demonstrated a weight of 32 02/YD² and OSU heatrelease values of: peak HRR=52.0 and 2 minute HRR=51.0, and a flexuralstrength value approximately three times greater than that of thecomposite of Example 1.

Other embodiments are within the following claims. For example,composite materials of the invention may be employed in the form of anystructural, non-weight bearing elements of an aircraft passengercompartment, e.g. wall and ceiling panels. In these and otherembodiments, the order of the composite layers may be varied as desiredaccording to the desired application. For example, in wall panels, wherethe non-woven layer is to be the passenger compartment side of the panelfor reasons of appearance, the metallic film may be applied upon thenylon film, e.g. as the opposite surface layer, in order to betterretard penetration of heat into the passenger compartment in the eventof a fire.

Also, multiple layers of non-woven and/or woven prepreg material may beemployed for adding bulk to the composite material, and thus increasingwall thickness and stiffness, where such characteristics are desired.

Although the foregoing describes several embodiments of a compositematerial of the invention, it is understood that the invention may bepracticed in still other forms, including but not limited to withgreater or fewer layers, still within the scope of the following claims.For example, the concept of the invention may be employed also inunderwater environments, i.e. in submarines, with similar performancerequirements for heat release, flammability, smoke release and/or toxicgas release.

What is claimed is:
 1. A composite material comprising a reinforcingpolymeric resin, and a plurality of felt layers impregnated with saidreinforcing polymeric resin, each felt layer comprising a plurality offibers having a predominant fiber direction, said felt layers beingarranged so that said predominant fiber direction of each layer is at atransverse angle with respect to the predominant fiber direction of theimmediately adjacent layers, at least one of said felt layers comprisinga needle entangled web.
 2. A composite material of claim 1 comprisingfour felt layers, each felt layer being disposed at a 90 degree anglewith respect to immediately adjacent felt layers.
 3. A compositematerial of claim 1 wherein each felt layer comprises from 30 to 34weight percent of a first reinforcing polymeric resin.
 4. A compositematerial of claim 1 further comprising an outer wall comprising afibrous non-woven web or fabric.
 5. A composite material of claim 4wherein said outer wall is coated or impregnated with a secondreinforcing polymeric resin and bonded to one of said felt layers.
 6. Acomposite material of claim 3 wherein said reinforcing polymeric resinis a phenolic resin.
 7. A composite material of claim 5 wherein eachsaid reinforcing polymeric resin is a phenolic resin.
 8. A compositematerial of claim 1 wherein said felt layer comprises fibers selectedfrom the group consisting of carbon, graphite, glass, aramid andmixtures thereof.
 9. A composite material of claim 8 wherein said feltlayer comprises predominantly aramid fibers.
 10. A composite material ofclaim 4 wherein said outer wall comprises a glass fabric or scrim.
 11. Acomposite material of claim 3, 5, 6 or 7 wherein said reinforcingpolymeric resin is a water-borne resin.
 12. A composite material ofclaim 5 wherein said first and second reinforcing polymeric resinscomprise the same polymer.
 13. A composite material of claim 1 or 4further comprising a barrier layer selected to render the compositeimpermeable to the flow of air.
 14. A composite material comprising alayer of felt material in a compressed state, and impregnated with areinforcing polymeric resin comprising a water-borne phenolic resin,said layer of felt material containing from 28 to 32 percent by weightof said reinforcing polymeric resin after the water carrier of saidwater-borne phenolic resin has been driven off.